The device is essentially a scaled-down version of the method used by the LIGO collaboration to detect gravitational waves made by colliding black holes. In this case, the gravimeter senses subtle changes in the strength of the gravitational fields generated by any object, using clouds of cold rubidium atoms as sensors. These clouds of atoms are held aloft in a basketball-sized vacuum chamber and cooled down to 80 microkelvin – barely above absolute zero.

The atoms are put into a superposition, where they’re in two states at once – think Schroedinger’s cat, both alive and dead – until a measurement is made. Then the atom clouds are dropped, and while in freefall, zapped with three laser pulses. Those pulses serve as a kind of ruler made of light, measuring the position at those key points in time before the clouds come back together to make what’s called an interference pattern.

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That pattern is much like what you’d see if you dropped two stones in a pond and they created separate ripples that cross and interfere with other. Here, it encodes the position of the atom clouds and their paths.

Spot the difference

If two atom clouds fall at different speeds, it would indicate a change in the density of the ground below. This could be due to the presence of oil or certain minerals, for example.

“Essentially it relies on the fact that any mass will generate a gravitational field, which can be detected with a very precise gravity sensor,” says Kai Bongs at the University of Birmingham, who helped develop the device.

Quantum effects disappear when exposed to any outside interference or noise, so any quantum system or device must be carefully shielded and cooled to very low temperatures. This has limited their use in many real-world applications. But times are changing.

“We’re starting to see this technology maturing into the commercial domain,” says Graeme Malcolm, founder and CEO of photonics company M Squared in Glasgow, which developed the gravimeter with a team at the University of Birmingham.

That’s why the oil and gas industry could be particularly interested in the gravimeter. It could be a powerful tool to help map out valuable deposits of oil or minerals, because denser materials will have a stronger gravitational pull than open pockets beneath the earth.

Construction companies could use the gravimeter to locate pipes buried deep underground, preventing the costs of accidentally digging up the wrong bits of road. Existing technology for this kind of geophysical mapping is bulky and difficult to use, and not as sensitive as a quantum gravimeter would be.

Shrinkable tech

“It provides them with a better view into the unknowns of the underworld,” says Bongs. It might one day even be used in seismic mapping, helping predict natural disasters like tsunamis or volcanic eruptions.

Because it uses laser cooling rather than bulky cryogenics, the gravimeter prototype is only about one cubic metre. In principle, it should be possible to shrink many of the components like the lasers and the vacuum chamber, to make it more portable, says Malcolm.

M Squared is also developing a quantum accelerometer that could augment GPS navigation to offset interference from bad weather. Other potential quantum devices might make it possible to “see” invisible gases. “I think we’re just at the early stage of commercial adoption of quantum technologies,” says Malcolm.

Spyridon Michalakis at the California Institute of Technology also thinks that the future is quantum.

“Quantum physics underlies so many of the technologies we take for granted today, but it is only recently that we have been able to exploit the quantum properties of many-body systems to arrive at insanely precise, low-cost and compact versions of previous tech, like gravimeters,” he says.

“Imagine what will be possible in the near future, when it gives us reliable and scalable quantum computers, cheap materials that levitate at room temperature, and quantum networks that teleport quantum information with unprecedented security guarantees through quantum teleportation.”